As he spun wildly, the ice shards enveloped by him were melting at a speed visible to the naked eye. The ice water had no chance of transforming into a Water Elemental Monarch at all; it was instantly vaporized. Some of it, like before, was expelled from the Fire Elemental Monarch's body in the form of high-temperature steam, while other parts were consumed internally and transformed into a part of the Fire Elemental Monarch's body.
Extremes meet.
This is illustrated to the extreme on these elemental creatures.
The reason for the severe hostility between Fire Elements and Water Elements, Air Elements and Earth Elements, is not only their elemental properties of mutual aid and counteraction, but also because each holds essential materials needed by the other. If these could be plundered, one could absorb more of the same type of elements, becoming stronger.
